Recent semiconductor elements to be incorporated in an inverter control device or other devices need to have higher densities and operate at higher speed. However, the increases in density and speed of semiconductor elements cause a rise in calorific values of the semiconductor elements, thereby creating the possibility of degradation in operational reliability of the semiconductor elements. In view of this, a heat dissipation structure incorporating semiconductor elements has become important.
For example, Patent Document 1 proposes a semiconductor device with a heat dissipation structure. As illustrated in FIG. 13, the semiconductor device of Patent Document 1 has a heat dissipation structure in which the back surface of a die pad 102 on which a semiconductor element 101 is mounted is exposed from an encapsulating resin 103.
Patent Document 2, for example, proposes another semiconductor device with a heat dissipation structure. As illustrated in FIG. 14, the semiconductor device of Patent Document 2 has a heat dissipation structure in which a die pad 202 on which a semiconductor element 201 having a large calorific value is mounted is connected to a heat dissipation member 203 and the heat dissipation member 203 is partially exposed from an encapsulating resin 204 sealing the semiconductor element 201.
In addition, Patent Document 3, for example, also proposes a semiconductor device. In the semiconductor device of Patent Document 3, a semiconductor element is mounted on a heat dissipation member including a first metal member of iron and a second metal member of copper penetrating the first metal member. This semiconductor device has a structure in which the semiconductor element is sealed by an encapsulating resin such that the heat dissipation member is partially exposed.
In operation of these conventional semiconductor devices, however, heat generated by the semiconductor elements increases the temperature, and a difference in thermal expansion coefficient causes thermal stress between the semiconductor element and the die pad or the heat dissipation member. This is because the thermal deformation amount of the die pad is larger than that of the semiconductor element. This thermal stress causes warpage of the semiconductor device. Accordingly, in addition to variation in characteristics of the semiconductor element, cracks occur in, for example, the semiconductor element, resulting in that reliability of the semiconductor device might degrade.
Patent Document 4, for example, proposes a semiconductor device with a structure for reducing thermal stress occurring in a semiconductor element. In the semiconductor device of Patent Document 4, part of a surface of a semiconductor element is supported by a columnar member to reduce thermal stress occurring in a semiconductor element, as compared to a case where the entire area of a surface of the semiconductor element is supported by, for example, a substrate.
Patent Document 5, for example, proposes a semiconductor device with a structure as described above to reduce thermal stress occurring in a semiconductor element and to release heat from the semiconductor element to the outside. As illustrated in FIG. 15, the semiconductor device of Patent Document 5 includes a heat dissipation member 306 provided on a metal substrate 301 of aluminium (Al) with an insulating layer 302 and solder 303 interposed therebetween. The heat dissipation member 306 is made of copper (Cu), and includes a plurality of columns 305 and a plate 304. A semiconductor element 308 is mounted on the columns 305 with solder 307 interposed therebetween. Heat generated in the semiconductor element 308 is transmitted from the columns 305 to the plate 304 through the solder 307, passes through the insulating layer 302, and is dissipated to the outside from the metal substrate 301. Here, copper constituting the heat dissipation member 306 and aluminium constituting the metal substrate 301 have thermal expansion coefficients larger than that of silicon dioxide (SiO2) constituting the semiconductor element 308. Accordingly, when the temperatures of these components increase, the difference in thermal deformation amount causes thermal stress to be applied on the solder 307 connecting the semiconductor element 308 and the columns 305, thereby causing the possibility of a split or a breakage. In Patent Document 5, a copper wire is employed for the columns 305 to have the strength of the columns 305 lower than that of the solder 307, and thereby, the columns 305 in bending states support the semiconductor element 308. According to Patent Document 5, the above structure hardly causes thermal stress, and thus, can prevent warpage of the semiconductor element 308 due to the thermal stress.